Antagonistic role of MBNL1 and LIN28 promotes specific alteration of pre-miR-1 processing and is associated with heart defects in DM. Homo sapiens

Myotonic dystrophy type 1 (DM1), the most common muscular dystrophy in adults, is caused by the expression of expanded CUG repeats, which sequester the MBNL1 RNA binding protein. Cardiac involvement, which is characterized by conduction defects and arrhythmias, is the second cause of death of DM1 patients. Down-expression of miR-1 in mice leads to cardiac conduction disturbances and to arrhythmias. Here, we show that miR-1 expression is decreased in DM1 hearts, due to a mis-regulation of the processing of pre-miR-1. MBNL1 binds to UGC motifs located within the pre-miR-1 loop and competes binding of LIN28, which promotes uridylation and blocks pre-miR-1 processing. Finally and consistent with a down-regulation of miR-1, known, GJA1, and novel, CACNA1C, targets of miR-1 are increased in DM1 hearts. CACNA1C and GJA1 encode the main calcium and gap junction channels in heart, respectively, and their mis-regulation may contribute to the heart arrythmias and conduction defects observed in DM1 patients. Overall design: Total RNA of 3 control and 3 CDM1 primary culture of muscle cells differentiated 10 days into myotubes was extracted using Trizol and analyzed by Agilent microarray.

1型强直性肌营养不良（Myotonic dystrophy type 1, DM1）是成人最常见的肌营养不良症，由扩增的CUG重复序列表达引发，该序列会螯合RNA结合蛋白MBNL1。以传导缺陷与心律失常为特征的心脏受累情况，是DM1患者的第二大死亡诱因。研究表明，小鼠体内miR-1表达下调可引发心脏传导紊乱及心律失常。本研究证实，DM1患者的心脏组织中miR-1表达水平降低，这一现象源于pre-miR-1的加工过程调控异常。MBNL1可结合pre-miR-1环区中的UGC基序，并与LIN28产生竞争，而LIN28能够促进尿苷酸化过程并阻断pre-miR-1的加工。最后，与miR-1表达下调的结论相符，已报道的miR-1靶基因GJA1以及新鉴定的miR-1靶基因CACNA1C，在DM1患者的心脏组织中表达上调。CACNA1C与GJA1分别编码心脏内主要的钙通道与间隙连接通道，二者的表达异常可能参与了DM1患者所出现的心脏心律失常与传导缺陷的病理过程。实验整体设计：提取3例对照样本与3例CDM1原代肌细胞培养物的总RNA，这些肌细胞经10天分化形成肌管，采用Trizol试剂完成提取后，通过安捷伦（Agilent）基因芯片进行分析。